/*
 * Copyright (C) 2012 Andrea Parodi
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package container;


import com.google.common.base.Optional;
import com.google.common.base.Preconditions;

public final class CheckDigitCalculator {


    private CheckDigitCalculator() {
    }


    private static int[] map = {10, 12, 13, 14,
            15, 16, 17, 18,
            19, 20, 21, 23,
            24, 25, 26, 27,
            28, 29, 30, 31,
            32, 34, 35, 36,
            37, 38};

    public static Optional<Integer> getCheckDigit(String cntrNumber) {
        try {
            Preconditions.checkNotNull(cntrNumber);

            int total = 0;

            for (int i = 0; i < 4; i++) {
                final int idxMap = Character.getNumericValue(cntrNumber.charAt(i)) - 10;
                if (idxMap < 0 || idxMap >= map.length)
                    return Optional.absent();

                total += map[idxMap] << i;
            }

            for (int i = 4; i < 10; i++) {
                total += Integer.parseInt(cntrNumber.substring(i, i + 1)) << i;
            }

            final int modulus = total % 11;
            return Optional.of(modulus == 10 ? 0 : modulus);
        } catch (NumberFormatException e) {
            return Optional.absent();
        }
    }


}
